A large number of semiconductor components (such as LSI chips) are used in the electronic devices currently on the market.
In normal circumstances, a semiconductor component is temporarily mounted on a wiring board (hereinafter also referred to as an interposer) for packaging, and the wiring board is connected, together with other parts and the like, onto a mother board.
Conventionally, a wiring board has a core member that is an organic substrate formed with glass epoxy, a silicon substrate made of silicon, or the like. However, with an organic substrate or a silicon substrate, it has been gradually becoming difficult to cope with reductions in the sizes of the semiconductor components. Therefore, a wiring board having a glass substrate as its core member is now often used so that the sizes of wirings can be reduced.
FIG. 1 shows an example structure of a through-electrode-equipped wiring board in which a glass substrate is used as the core member. As shown in the drawing, in a through-electrode-equipped wiring board 10, a glass substrate 13 is used as the core member, and wiring layers 12 and 15 are formed on both surfaces of the glass substrate 13. Further, through electrodes 14 filled with a conductive metal such as copper (Cu) are provided in the glass substrate 13, and the wiring layers 12 and 15 are electrically connected to each other by the through electrodes 14. Semiconductor components 16 are connected to the wiring layer 12.
As described above, as the glass substrate 13 is used as the core member, the wirings can be made smaller in size in the through-electrode-equipped wiring board 10. In the through-electrode-equipped wiring board 10, however, problems of stress and heat release might be caused by the material (glass) of the core member and the material (Cu in this case) of the through electrodes 14.
As for a specific example of the problem of stress, cracks might be caused in the glass substrate 13 by the stress generated due to the existence of a one-digit difference in coefficient of linear expansion (CTE) between the glass substrate 13 and the through electrodes (Cu) 14 during the high-temperature process performed to form the wiring layers 12 and 15 and mount the semiconductor components 16 onto the glass substrate 13.
CTE of glass: 7.5 [10−6/K]
CTE of Cu: 14.3 [10−6/K]
As for a specific example of the problem of heat release, the heat release rate of glass is lower than that of silicon, and therefore, the heat release that can be conducted in a case where a silicon substrate is used cannot be appropriately conducted in a case where a glass substrate is used. This causes failure.
Thermal expansion rate of silicon: 188 [W/mK]
Thermal expansion rate of glass: 1 [W/mK]
It should be noted that, to solve the problem of stress, a method has been suggested. According to this method, a metal paste that has a small CTE difference from glass and is formed with metal particles, a resin binder, and a solvent is used as the material of the through electrodes to be formed in a glass substrate (see Patent Document 1, for example).
Meanwhile, to solve the problem of heat release, there has been a suggested method by which dummy through electrodes that function as a heat dissipation path are used as well as active through electrodes that function as an electrical connection path (see Patent Document 2, for example).